Wikimedia Bugzilla is closed!

This is the DOM returned by the VE after inserting a new thumbnail:

<figure typeof="mw:Image/Frame" class=" mw-halign-right"><a rel="mw:thumb" href="http://commons.wikimedia.org/wiki/File:Apples.jpg"><img src="http://upload.wikimedia.org/wikipedia/commons/thumb/e/ee/Apples.jpg/100px-Apples.jpg" width="100" height="150" resource="undefined"></a></figure>

Note the 'undefined' in the resource attribute. The resource is the image target, so we notice that the link and the image named 'undefined' differ and serialize as [[undefined|link=http://commons.wikimedia.org/wiki/File:Apples.jpg|thumb]].